The Dash (Density And Scale Height) satellites were 2.5-m-diameter balloons used to measure air densities at altitudes of approximately 3500 km. The area-to-mass ratio for the spacecraft was 40 sq ... cm/g. The orbit, originally circular, increased in eccentricity rapidly under the action of solar radiation pressure. This experiment used the variations in orbit characteristics of the Dash balloon satellite to deduce neutral air densities and to study the effect of solar radiation pressure. Other effects, such as terrestrial radiation pressure, lunar gravity, and solar gravity were also observable.